Friday, February 22, 2008

Many pro-inflammatory molecules share the intracellular signaling pathway with Nuclear Factor – kappa Binding (NF-kB) for their induction and activity. Cytoplasmic NF-kB is released and transported into the nucleus, where it drives transcription of specific genes, when an inhibitor (IkB) is phosphorylated by the inhibitor-kappa kinase beta (IKKb) The importance of this pathway suggests that IKKb would be a promising target for new anti-inflammatory drugs. Here, Greten and colleages tested this idea using mice in which IKKb was deleted in myeloid cells: macrophages and neutrophils (IKKb-del-myo). [A total IKKb deficiency is an embryonic lethal]. IKKb-del-myo mice were viable and had no obvious changes even within tissues that are rich in myeloid cells, such as lymphoid organs and the gastrointestinal tract. They observed that IKKb-del-myo mice were actually more susceptible to endotoxin- (LPS-) induced toxic shock, which is mediated by TNF and interleukin-1beta (IL-1b). IKKb-deficient cells are more susceptible to apoptosis because some NF-kB-induced genes are protective (e.g., A20).The authors also studied another conditional knockout mouse, in which IKKb is deleted in all “interferon-inducible” cells (IKKb-del), though this model is complicated by a requisite induction with the pleiotropic agent poly-I:C and deletion probably occurs in many more cell types. These mice develop many more granulocytes and, like the IKKb-del-myo mice, also produced much higher levels of IL-1b after LPS treatment. However, mRNA encoding IL-1 was actually decreased, suggesting a change in IL-1 processing.

Indeed, the authors determined that NF-kB inhibits caspase-1 and serine proteases that are required in macrophages and neutrophils, respectively, to cleave pro-IL-1b and release the active cytokine. Consistent with this interpretation, a serine protease inhibitor protected mice against IL-1b-induced death. Mice exposed to LPS die more quickly and more often when fed ML120B, an inhibitor of IKKb for a protracted period with multiple doses, correlating with an increased processing and release of IL-1b (figure, extracted from Figure 7). Definitely not a lead compound for a daily regimen.Greten et al. Cell. 2007 Sep 7;130(5):918-31. "NF-kappaB is a negative regulator of IL-1beta secretion as revealed by genetic and pharmacological inhibition of IKKbeta"

Monday, February 18, 2008

This paper reminds me of an old joke: when a patient, having received a dubious diagnosis, asks for a second opinion, the doctor replies 'you're also ugly'. But seriously, folks, this paper suggests that the rise of obesity in the US could have unanticipated consequences for infectious disease. To test the effect of obesity on immunity, Amar and colleagues infected fat or lean mice with Porphyromonas gingivalis, a bacterium that causes gum disease. Mice fed with high fat food for 4 months weighed about 30% more than the mice on normal chow.They found that mice with diet-induced obesity (DIO) suffered a greater loss of alveolar (gum) bone than did lean mice. P. gingivalis infection induced less inflammatory cytokine release in DIO mice than in lean mice. Macrophages cultured from DIO mice showed significantly reduced activation by LPS of the intracellular signaling molecule NF-kappaB (a chromosome immunoprecipitation is shown, from Fig. 8). Oddly, C-reactive protein, a marker of inflammation, is reported elevated in the bloodstream of obese humans. Do you have a 'second opinion'?Amar et al., Diet-induced obesity in mice causes changes in immune responses and bone loss manifested by bacterial challenge. Proc Natl Acad Sci U S A. 2007 Dec 18;104(51):20466-71.

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